microsoft / microsoft/STL

P2944R3 Comparisons For `reference_wrapper`

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cxx26 spaceship
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Description

WG21-P2944R3 Comparisons For reference_wrapper
WG21-P3379R0 Constrain expected Equality Operators
LWG-4071 reference_wrapper comparisons are not SFINAE-friendly
LWG-4072 std::optional comparisons: constrain harder

Also tracked by #5873 (this is half "implement downlevel", half "patch C++26"):
LWG-4366 Heterogeneous comparison of expected may be ill-formed

Feature-test macros:

#define __cpp_lib_constrained_equality 202411L
#define __cpp_lib_reference_wrapper    202403L

Note: We are not yet accepting PRs for C++26 features.

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reading WG21-P2944R3 and WG21-P3379R0 alongside LWG-4071, LWG-4072, and LWG-4366; issue #5873 tracks related work. The issue lists expected feature-test macros, but provides no files, tests, or implementation entry points, and states that PRs for C++26 features are not yet being accepted.

Written by the indexing model from the issue text.

Assessment

Tech stack
cpp
Domain
devtools
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
15/100

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